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Wire restraint in ICF construction

moltenmetal | Posted in Energy, Heating & Insulation on December 19, 2005 11:12am

Hi All:

Did a search and didn’t find a satisfactory answer to this question:

When installing outlet boxes in ICF construction, what do you do to meet the code rule for a wire staple within 8″ of the box? 

Attaching the box to the web in the ICF form or to the concrete using Tapcons etc. is no problem.  There’s a strain relief in each box, which in combination with the wire foamed into a chainsawed kerf in the foam, should ensure that there’s no way the wire could go anywhere.  But I’m sure the inspector will still want to see some kind of wire restraint to the “structure” to replace that stupid staple.  In my experience, inspectors quote code chapter and verse and check their commonsense at the door:  they’re not paid to think, nor to accept the liability that comes along with thinking.

Your thoughts as always will be greatly appreciated!

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Replies

  1. PeteVa | Dec 19, 2005 11:38pm | #1

    I use EMT to go from box to box to give me wire protection from any future wall penetrations. The EMT is foamed into chanels cut into the ICFs. My inspector is quite content with that arangement. If your's has a question about it's strength make him a a test piece from a scrap and see if he can get the EMT to seperate from the ICF.

    1. moltenmetal | Dec 20, 2005 12:01am | #2

      Thanks for the response.  So- your solution was to run EMT conduit in the foam, and then pull conduit wire instead of using nonmetallic sheathed cable?  Or did you run NMD90 inside the EMT, using the EMT as a sort of chase-way? (is that allowed?  Does it have to be de-rated under those conditions?)  

      Guess that's one way to keep the inspector happy!  I guess I could just run BX flexible armoured cable in a saw kerf in the foam as an alternative- but I don't want to do that either, and that too requires a wire restraint within a certain distance of the box, right?. 

      I'd rather scoop out a chunk of foam, screw a block of wood between two ICF webs, and drive a staple into the wood, but I don't want to do that if I can avoid it.

      Any other suggestions out there?!

      1. PeteVa | Dec 20, 2005 12:09am | #3

        Yes I just pull THHN and treat the whole project as a Cook county, Ill wiring job. : )

    2. caseyr | Dec 20, 2005 07:39am | #6

      How do you go about making the channel fit the EMT (I assume you do it that way). Do you hold the bent (if necessary) EMT to the wall and mark where it goes and then freehand route out the channel?

      1. PeteVa | Dec 20, 2005 02:54pm | #9

        They sell a hotwire cutter for the purpose but I bought a $30 electric chain saw that I use.

  2. davemica | Dec 20, 2005 03:28am | #4

    The easiest way to secure the romex cable is just to save some of the foam scraps you cut out of the channel you made with the hot knife and just squeeze it back in every foot or two over the romex. Another way is to tapcon a one hole cable tie to the concrete and secure the romex with that. I find tapcon'ing the box to the concrete to be the most solid way to hold the box to the wall. The alternative is to buy boxes with face mount flanges and drywall screw them to the plastic "studs" in the foam. The screws dont really hold too solidly to the plastic studs though.

  3. Brian | Dec 20, 2005 04:33am | #5

    I foamed a dab within 6" of every box, and the inspection is tomorrow.  Our inspector is proud of his 90% fail rate...I'll post the results tomorrow.

     

    Treat every person you meet like you will know them the rest of your life - you just might!
  4. alwaysoverbudget | Dec 20, 2005 08:19am | #7

    i had them approved by just foaming in the channel every 3' or so.it's kinda new stuff to the inspectors so they still are working out what they want to see. larry

    hand me the chainsaw, i need to trim the casing just a hair.

    1. DaveRicheson | Dec 20, 2005 02:27pm | #8

      If you are hanging dw over ICF walls how do you meet the 1 1/4" from the face of the stud requirement for wire protection?

      I have seen more failed inspection for not meeting that single requirement than for not securing the wire within 8" of the box. I know that hanging dw over ICFs, in most cases, demands a very specific screw location, and it would be easy to route the wire around those points, but do the inspectors know that?

       

      Dave

    2. moltenmetal | Dec 20, 2005 04:34pm | #10

      My ICF consultant says that he just installs an 2 1/2" airtight flanged box attached to a web with drywall screws, chainsaws a kerf for the wire and runs the wire, and hasn't had any problems with local inspections.  He doesn't install any additional wire restraint.

      I like your method- the dot of can foam every 3' will permit the inspector to still pull out the wire for inspection if he wants to, but secures it enough that he can see that the wire isn't going to fall out on its own.

      No problem with the 1.25" depth requirement- the foam is 2.5" thick.

      1. Brian | Dec 21, 2005 05:22am | #11

        We passed the inspection today - the inspector had never seen ICFs - once he heard the ICF foam was 2.5" deep he gave it no more thought.  I explained why the foam was dabbed here and there and he kinda shrugged and went on.

        So we've cleared another hurdle I was worried about...

        My thinking is that if a hole in a stud within 6" of a box counts as support, then certainly a wire snuggly stuffed in a chainsaw kerf should count.

         Treat every person you meet like you will know them the rest of your life - you just might!

        1. PeteVa | Dec 21, 2005 05:34am | #12

          Congratz!!!!!!!!!!!!

        2. alwaysoverbudget | Dec 21, 2005 09:16am | #13

          that was our experence,the inspector wasn't familer enough with icf's,so somethings he would approve and some we had to work with him. the biggest problem we had was attaching the base mldg trim. have you thought about that yet? if i was doing another one i would run the sheetrock  up 2.5" off the floor and fill with 1/2 wood screwed to the webs. that would give me something to shoot the nails into. by the time you finish sheetrock those webs dissappear!larryhand me the chainsaw, i need to trim the casing just a hair.

          1. Brian | Dec 22, 2005 04:11am | #15

            I was thinking ripped plywood for the bottom 2.5" too - just for baseboard installation.  I don't think the plastic webs would hold a trim nail too well.

            I double plated the interior walls on the bottom too, for the same reason, although my builder friends all think the top should be doubled... (non load walls)

             Treat every person you meet like you will know them the rest of your life - you just might!

        3. moltenmetal | Dec 21, 2005 03:45pm | #14

          Great- thanks for letting me know.

          Those PVC "airtight" flanged boxes at 2.5" deep are a perfect fit.  Cut the foam with a recip saw, popped the foam out with the claw of the hammer and fastened the box to the web with two screws- the boxes are really secure even without foaming them in place.  No need for Tapcons into the concrete etc.  Just the long chainsaw cut to do yet.

          1. Brian | Dec 22, 2005 04:14am | #16

            I was glad to find the 2.5" boxes at lowes - my plans were to use metal boxes tapconned in - so glad I found the flanged plastic model.

            I tried to drive a concrete nail through a round box that needed fastening - it shattered.  So I foamed everything in place - took 10 minutes to do the entire house - and the inspector had no issues w/ICFs.

             Treat every person you meet like you will know them the rest of your life - you just might!

          2. moltenmetal | Dec 22, 2005 04:27pm | #17

            I chainsawed the kerfs for the wire and installed the wire last night after work.  A good trick:  use the seam between two layers of ICF blocks as the place to run your wire.  Since the ICF webs stop short of the top and bottom of the ICF blocks, there are no webs in this seam area, so there are no webs to chainsaw through.  That makes both the cutting and the wire-stuffing easier, especially with 3-wire, because there are no webs to snag the wire as you stuff it in place.

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